This disclosure pertains to organic waste processing. More particularly, this disclosure pertains to a method and apparatus for processing biodegradable organic waste in an aqueous medium. The disclosure also pertains to an apparatus and process for determining the biochemical oxygen demand (BOD) of an organic waste in an aqueous medium.
A variety of methods for the disposal of organic waste, either industrial or agricultural, are available. Some of these methods, such as burial, land-fill, dumping at sea, and the like, have a negative environmental impact and are not desirable. On the other hand, methods are available for converting organic waste to a source of energy and/or a usable product and include, among others, biological aerobic fermentation, biological anaerobic fermentation, thermophilic aerobic digestion, destructive distillation (including hydrocarbonization and pyrolysis), and incineration. W. J. Jewell et al., "Methane Generation from Agricultural Wastes:Review of Concept and Future Applications", Paper No. NA74-107, presented at the 1974 Northeast Regional Meeting of the American Society of Agricultural Engineers, West Virginia University, Morgantown, West Virginia, Aug. 18-21, 1974. Of this latter group, biological anaerobic fermentation appears to be the most promising and has received considerable attention in recent years.
Current interest in biological anaerobic fermentation appears to be due, at least in part, to the development of the anaerobic filter. See, for example, J. C. Young et al., Jour. Water Poll. Control Fed., 41, R160 (1969); P. L. McCarty, "Anaerobic Processes", a paper presented at the Birmingham Short Course on Design Aspects of Biological Treatment, International Association of Water Pollution Research, Birmingham, England, Sept. 18, 1974; and J. C. Jennett et al., Jour. Water Poll. Control Fed., 47, 104 (1975). The anaerobic filter basically is a rock-filled bed similar to an aerobic trickling filter. In the anaerobic filter, however, the waste is distributed across the bottom of the filter. The flow of waste is upward through the bed of rocks so that the bed is completely submerged. Anaerobic microorganisms accumulate in the void spaces between the rocks and provide a large, active biological mass. The effluent typically is essentially free of biological solids. See J. C. Young et al., supra at R160.
The anaerobic filter, however, is best suited for the treatment of water-soluble organic waste. J. C. Young et al., supra at R160 and R171. Furthermore, very long retention times of the waste in the filter are required in order to achieve high reductions in the chemical oxygen demand (COD) of the waste to be treated. That is, depending upon the COD of the waste stream, reductions in such COD of from 36.7 percent to 93.4 percent required retention times of from 4.5 hours to 72 hours. J. C. Young et al., supra at R167. In addition, such results were achieved with optimized synthetic wastes which were balanced in carbon, nitrogen, and phosphorus content and which had carefully adjusted pH values.
Accordingly, there remains a great need for a waste processing method which can tolerate the presence of solids in the waste stream and which can more rapidly process the waste on an "as is" basis.